Physiology
Gastrointestinal
Where in the body is most iron absorbed:
Answer:
Iron is absorbed mainly in the duodenum and jejunum.Iron Handling
Physiology / Gastrointestinal / Small Intestine
Last Updated: 21st April 2019
The total amount of iron in the body is about 3 - 4 g, of which about two-thirds is in haemoglobin.
Iron Absorption
Iron exists in two forms, the ferrous state (Fe2+) or the ferric state (Fe3+). Most dietary iron is in the form Fe3+, which is reduced by ferrireductase in the mucosa assisted by ascorbic acid and HCl in gastric secretions to the more soluble Fe2+ and then absorbed by the duodenum and jejunum.
Fe2+ is taken across the enterocyte apical membrane by the divalent metal transporter (DMT1). In the enterocyte, Fe2+ is oxidised to Fe3+ and then either stored in enterocyte epithelial cells bound to apoferritin, or released into the plasma via the molecule ferroportin on the basolateral membrane.
Iron Transport
Iron in the plasma is bound to the transport protein transferrin. Iron is transferred to the bone marrow for erythropoiesis or to the liver or other parenchymal cells for storage as ferritin or haemosiderin. The iron released from the breakdown of senescent red blood cells, some of which is stored by the macrophages in the liver and spleen, provides most of the iron on transferrin, only a small proportion of transferrin iron comes from dietary iron.
Regulation of Iron Absorption
The normal Western diet contains about 10 - 20 mg of iron per day and typically about 5 - 10% of this is absorbed (to replace that lost by intestinal epithelial cell shedding). Iron absorption is tightly regulated as excess iron is potentially toxic, and the body has no physiological mechanism for upregulating excretion.
Iron absorption can be increased when body stores are low or when there is a need to increase erythropoiesis e.g. an increase in absorption may be seen about 3 - 4 days following haemorrhage.
Hepcidin is the main hormonal regulator of iron homeostasis; it inhibits iron release from macrophages in the reticuloendothelial system and from intestinal epithelial cells and inhibits intestinal iron absorption. Hepcidin is suppressed by erythropoietin, ineffective erythropoiesis, pregnancy and hypoxia, but upregulated in inflammation and iron overload.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
